Infrared (IR) radiation is emitted as radiant heat from all physical objects above absolute zero temperature. The ideal example of an IR emitter is a perfect black body which neither reflects nor transmits energy impinging upon it, but rather absorbs all energy impinging upon it, The black body, at steady state, then re-emits this absorbed energy in frequencies dependant on the temperature of that black body. A theoretically perfect black body has an emissivity of 100%, a reflectivity of 0%, and a transmissivity of 0%.
Emitted IR energy has been studied for apparent benefits to living tissue. IR appears to enhance vital biological activity, such as expanding microcapillaries to enhance blood flow, boosting blood oxygen levels, and improving nutrient transport in and out of cells.
There is interest in materials that are close to black bodies in that they can absorb ambient energy from sources such as sunlight, artificial light, body heat, other ambient heat, electromagnetic energy, etc. and then, at steady state, re-emit this energy. Of particular interest are materials that emit IR energy, particularly in the 4 to 14 micron wavelength range of the far infrared spectrum, which is thought to be especially beneficial. Such materials that emit energy in this way may be very beneficial in enhancing healthy biological activity in living tissue. There is evidence, for instance, that packaging materials containing these IR-emitting materials aid in maintaining and lengthening the freshness of foodstuffs such as fresh produce and meat products. There is also evidence that garments, medical devices, blankets, and other such durable goods may enhance the physical health and well-being of living creatures including humans. Such durable goods have been shown to reduce inflammation, enhance blood oxygenation and other natural health-inducing biological functions, and improve performance during physical exertion such as exercise and sports. For these reasons, IR-emitting materials are sometimes described as being ‘bio-active’ and possessing ‘bioactivity.’
Suitable IR-emitting materials come from many sources. Various natural minerals and other inorganic materials have been shown to exhibit IR-emitting properties. Some organic materials also have these properties. It has been found that the IR materials work best when pulverized into fine powders including nano-sized particles, which increases the surface area of the solids. The powders can be applied to the surfaces of base materials, such as fabrics, films or other solid objects. The powders can also be mixed into coatings or paints and applied to the surfaces of solid objects. The powders can also be mixed into a liquid or molten matrix, such as a molten thermoplastic polymer, and then molded into useful objects.
However, these IR-emitting materials have drawbacks. These materials can be difficult to incorporate into consumer goods. As noted above, these materials are most effective when pulverized into fine powders. Incorporating such powders into consumer goods can present challenges. Mineral-based or inorganic IR powders do not have a natural affinity for the organic materials used in most consumer goods. For garments, IR-emitting powders can be sprayed onto the surface of natural fibers, such as cotton, linen, and wool, but these powders can be removed or lost due to abrasion during wear or when washing the garment. Incorporating IR powders into synthetic polymers is feasible. But there is a limit to how much IR powder can be blended into a thin polymer material like a spun fiber or thin film before the polymeric material can no longer be manufactured. For instance, it has been found that inorganic IR-emitting powders can be successfully blended into continuous spunbonded polymeric fibers at concentrations of no more than about 2-5% before the fiber becomes too easily broken during manufacture. It is unclear if garments, drapes, blankets, bandages, and other such consumer goods containing such a low level of IR-emitting powders are as effective in providing the health benefits that these materials promise.
FIR-emitting fabrics in the market today generally include woven and knit fabrics made of spun yarns, and such fabrics have limited bio-activity as described below.
In these knit or woven fabrics, the minimum fiber diameter, as well as the maximum bio-active solids loading, is limited, due to the limitations of the fiber spinning process. For example, in order for the spun fibers not to break, the fiber sizes are typically over about ten microns in diameter, and the bio-active solids loading are no more than ˜2-5 wt. percent. If the solids loading is increased above this amount, even when a substantial portion of the particles are sub-micron in size, fibers cannot be spun without breaking. Therefore, there is a need to find a way to increase the solids loading in a fibrous web, so that higher levels of bioactivity can be attained in a soft, breathable and quiet fibrous material. There is also a need to find a way to lower the fiber diameters, which exposes the infrared emitting particles further, increasing both comfort and bioactivity.
Previous solutions to increasing the bioactivity of fibrous webs include making the IR powders as small as possible, which is reported to increase the bioactivity of the materials, as measured by measuring the emissivity of the powder additive or of the bioactive web. However, small particles, when added to a polymer carrier, can cause polymer processing problems, such as particle agglomeration and high viscosity, causing spun fiber breaks and other issues, especially at loadings of over 2-5 percent solids. So there is a practical limit to how small the particles can be, and how much can be added, in spun fibers, as well as a limit to the minimum fiber diameter.
Thus, it is desirable to look at other methods to improve bioactivity that can work in conjunction with making the particles smaller. Such methods include increasing surface area of the fiber and increasing the percent solids. This invention teaches a method to do this by providing a web of fibers with smaller diameters, high solid loadings and optionally with a textured surface.